Analysis of Nitrification Efficiency and Microbial Community in a Membrane Bioreactor Fed with Low COD/N-Ratio Wastewater

Abstract

In this study, an approach using influent COD/N ratio reduction was employed to improve process performance and nitrification efficiency in a membrane bioreactor (MBR). Besides sludge reduction, membrane fouling alleviation was observed during 330 d operation, which was attributed to the decreased production of soluble microbial products (SMP) and efficient carbon metabolism in the autotrophic nitrifying community. 454 high-throughput 16S rRNA gene pyrosequencing revealed that the diversity of microbial sequences was mainly determined by the feed characteristics, and that microbes could derive energy by switching to a more autotrophic metabolism to resist the environmental stress. The enrichment of nitrifiers in an MBR with a low COD/N-ratio demonstrated that this condition stimulated nitrification, and that the community distribution of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) resulted in faster nitrite uptake rates. Further, ammonia oxidation was the rate-limiting step during the full nitrification.

Soil Bacterial Biodiversity in Development of Secondary Loggedover Forest to Oil Palm Plantation in Mineral Soil of Belaga, Sarawak

“…Several studies indicated that soil bacterial community shifts after rainforest conversion were caused by fertiliser application, liming and reduction of plant diversity (Abdi et al, 2016;Val-Moraes et al, 2016;Liu et al, 2017). We also detected the nitrification-related phylum Nitrospirae with genus Nitrospirales in oil palm aged 3.5 years, where this genus is exclusively found in the oil palm plantations (Lücker et al, 2010;Ma et al, 2013). This genus signifies higher degrees of nitrification in oil palm soils compared to rainforest, probably caused by fertiliser application and correspondingly nitrogen input, leading to more favourable conditions for nitrifiers (Ma et al, 2013;Quan et al, 2016).…”

“…We also detected the nitrification-related phylum Nitrospirae with genus Nitrospirales in oil palm aged 3.5 years, where this genus is exclusively found in the oil palm plantations (Lücker et al, 2010;Ma et al, 2013). This genus signifies higher degrees of nitrification in oil palm soils compared to rainforest, probably caused by fertiliser application and correspondingly nitrogen input, leading to more favourable conditions for nitrifiers (Ma et al, 2013;Quan et al, 2016). The fertiliser regime increased certain bacteria population such as Firmicutes which was prevalent in the oil palm area with 1.5-year old palms where the application of fertiliser increased the pH and phosphate level in the soil ( Table 5).…”

Sustained organic loading disturbance favors nitrite accumulation in bioreactors with variable resistance, recovery and resilience of nitrification and nitrifiers

“…Also, nitrite accumulation was reported at low C:N values in studies using a 35-L SBR (~2 mg COD/mg TN) [39], a lab-scale 6.3-L SBR (3.33 mg COD/mg NH4 + -N) [41], and a pilot-scale continuous-flow A/O/A reactor (3.19 mg COD/mg NH4 + -N) [40]. On the other hand, there was complete nitrification without nitrite accumulation at low influent C:N (3 ± 1 mg COD/mg TN) in pilot-scale membrane batch reactors [38], similar to our results. Increasing C:N molar ratios from 2 to 5 was shown to significantly reduce nitrification rates in a laboratory denitrification-nitrification system [71], although the study did not mention whether this caused nitrite accumulation.…”

“…Influent manipulation in particular has been reported to yield contrasting results in terms of C:N [37]. Low influent C:N values (2-3 mg COD/mg TN) have been shown to prevent [38], but also promote [39][40][41] nitrite accumulation in different sludge systems. Other studies have reported nitrite accumulation at high (10 mg COD/mg NH4 + -N) [42] and also fluctuating influent C:N values (2.5-8 mg COD/mg NH4 + -N) [43,44].…”

Activity enhancement of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria in activated sludge process: metabolite reduction and CO2 mitigation intensification process

“…Under different operational conditions such as HRT, SRT, DO concentration, temperature, and substrate concentration the responses of autotrophic nitrifiers are divergent, which in turn influence metabolite production (Hu et al 2003). In low C/N ratios, nitrifiers dominate heterotrophs and enhance the nitrification efficiency (Ma et al 2013). Ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), contributors of two phylogenetically unassociated congregations of lithoautotrophic bacteria, perform nitrification process via a symbiosis interaction.…”